Laminate of polyimide film and inorganic substrate

Abstract

The invention provides a laminate including a polyimide film and an inorganic substrate, which has a number density of blisters including carbide particles therein of 50 /m 2 or less, an average height of blisters of 2 μm or less, a product of the number density of the blisters (blisters/m 2 ) and the average height of the blisters (μm) of 20 or less. The inventive laminate can be obtained by laminating the polyimide film and the inorganic substrate after sufficiently purifying and cleaning to remove foreign bodies made of inorganic substance therefrom, followed by heat treating the laminate at a temperature of 350-600° C. and then rapidly cooling it to carbonize and reduce the organic foreign bodies, and also to rapidly cool the gas contained in the blisters, which leads to reduced height of blisters.

The invention claimed is: 
     
       1. A laminate comprising a polyimide film and an inorganic substrate, characterized in that the laminate satisfies conditions (a) and (b):
 (a) a number density of blisters is 6/m 2  or more and 50/m 2  or less, an average height of blisters is 2 μm or less, and a product of the number density of blisters (blisters/m 2 ) and the average height of blisters (μm) is 20 or less; and 
 (b) a number density of blisters having a height of 3 μm or more is 10/m 2  or less, 
 wherein the blisters are formed by foreign bodies present between the polyimide film and the inorganic substrate and the foreign bodies contained inside the blisters are carbide particles. 
 
     
     
       2. The laminate comprising a polyimide film and an inorganic substrate according to  claim 1 , wherein the laminate has an area of 0.157 m 2  or more. 
     
     
       3. The laminate comprising a polyimide film and an inorganic substrate according to  claim 2 , further comprising a silane coupling agent condensate layer having a thickness of 5 nm to 500 nm between the polyimide film and the inorganic substrate. 
     
     
       4. The laminate comprising a polyimide film and an inorganic substrate according to  claim 1 , further comprising a silane coupling agent condensate layer having a thickness of 5 nm to 500 nm between the polyimide film and the inorganic substrate. 
     
     
       5. The laminate comprising a polyimide film and an inorganic substrate according to  claim 1 , wherein the laminate is obtained by imidizing a polyimide precursor to convert the polyimide precursor into the polyimide film and then laminating the polyimide film and the inorganic substrate. 
     
     
       6. The laminate comprising a polyimide film and an inorganic substrate according to  claim 1 , wherein the blisters comprise voids between the polyimide film and the inorganic substrate, which are caused by swelling of the polyimide film. 
     
     
       7. A method for producing the laminate comprising a polyimide film and an inorganic substrate according to  claim 1 , the method comprising the steps in the sequence set forth:
 laminating a polyimide film and an inorganic substrate; 
 subjecting the resulting laminate to a heat treatment at a temperature of 350° C. or more and less than 600° C. 
 
     
     
       8. The method for producing the laminate comprising a polyimide film and an inorganic substrate according to  claim 7 , further comprising, after the heat treatment, cooling the laminate at a rate of 10° C./min or more and 90° C./min or less to at least 200° C. 
     
     
       9. The method for producing the laminate comprising a polyimide film and an inorganic substrate according to  claim 8 , further comprising, as a pre-process before laminating a polyimide film and an inorganic substrate, washing the polyimide film with ultrapure water pretreated with ozone. 
     
     
       10. The method for producing the laminate comprising a polyimide film and an inorganic substrate according to  claim 7 , further comprising, as a pre-process before laminating a polyimide film and an inorganic substrate, washing the polyimide film with ultrapure water pretreated with ozone.